'downiness' originates from English, specifically from the adjective 'downy' (formed from the noun 'down' plus the adjectival suffix '-y'), where 'down' meant 'soft feathers' and '-y' meant 'characterized by'.

'downiness' changed from Old English 'dūn' (Middle English 'doun'/'down'), passed into English as 'down' meaning 'soft feathers', then formed the adjective 'downy', and eventually the noun 'downiness' by adding the suffix '-ness'.

Initially, the root 'down' meant 'soft feathers'; over time this sense extended to describe a texture or quality, leading to the modern meaning 'the quality of being downy (soft, fluffy)'.